The broad objective of the proposed research program is to assess the contribution of the frontal lobes to human memory. Behavioral analyses of neurological patients will be used to provide an understanding of neural systems underlying cognitive function. In the proposed studies, patients with frontal lobe lesions will be evaluated on a variety of memory and cognitive measures. Recently, the role of the frontal lobes in human memory and cognition has been studied rather extensively. Advances in the field have been attained by progress in human functional neuroimaging techniques, in cognitive analyses of patients with frontal lobe lesions, and in neurobehavioral analyses of animal models. These advances have led to the hypothesis that the frontal lobes contribute to "working memory"-that is, the on-line monitoring and controlling of information processing. The proposed research program will assess a theoretical framework that attempts to refine and extend the notion of working memory. It is suggested that the prefrontal cortex acts as a dynamic filtering mechanism that gates and ultimately controls stimulus encoding and memory activation. Damage to this mechanism results in a failure to filter inappropriate stimulus features, memories, and response decisions. In the proposed studies, patients with lesions of the dorsolateral prefrontal cortex will be evaluated on a variety of tests that tap aspects of attention and memory. These patients will be compared to neurologically intact control subjects and to other neurological patients (e.g., patients with orbital prefrontal lesions or temporal-parietal lesions). Central research questions include the following: What is the relationship between memory and other cognitive disorders observed in patients with frontal lobe lesions? At what stage or stages of memory processing do the frontal lobes appear to make significant contributions-stimulus encoding, access to semantic memory, memory storage, memory retrieval? As a result of an impairment in gating or selection, are patients with frontal lobe lesions more susceptible to interference from irrelevant or extraneous information?